Adrian Grant Duff was born in London on 29 September 1869, the son of Sir Mountstuart Elphinstone Grant Duff and Anna Julia Grant Duff (née Webster). He was educated at Wellington College and the Royal Military College, Sandhurst. On 22 October 1906, he married Ursula Lubbock, the daughter of John Lubbock, 1st Baron Avebury, with whom he had one son and three daughters.

On 23 March 1889, he was commissioned Second Lieutenant in the Black Watch and thereafter was promoted Lieutenant, in 1890, and Captain, in 1898. He served with the Black Watch in India, 1897-8, where he was commandant of the base depot during the Tirah Expedition, and in South Africa, 1902, where he saw action in the Transvaal during the final stages of the South African War.

After attending the Staff College, Camberley, 1903-4, he was appointed to the War Office as a Staff Captain, 1905, and later Quatermaster-General and General Staff Officer Grade 2, 1906. He was promoted Major, in 1907, and appointed Assistant Military Secretary to the Committee of Imperial Defence, in 1910, working on the 'war book' of procedures to be followed by government departments in the event of war.

In 1913, he rejoined the Black Watch at Aldershot, taking command of the 1st Battalion with the rank of Lieutenant-Colonel, in May 1914. He was killed in action at the Battle of the Aisne on 21 September 1914.

He was awarded the CB in 1913.